Distribution of Metals in a Mine Impacted Soil.

In wetlands, translocation of Fe and Mn from reducing to oxidizing zones creates localized enrichments and depletions of oxide minerals. In zones of enrichment, oxides cement matrix particles together into aggregates. Distribution of contaminants can be impacted by these redox gradients. In this presentation, we describe the various Fe- and Mn-cemented features present in the 1 to 2-mm size fraction of mine-waste contaminated wetland soils of the Coeur d’Alene River Basin in northern Idaho. In addition we will discuss the distribution of As, Pb, Zn, and Cd with respect to the redox features. Aggregate distribution in soil profiles along an elevation transect with varying water table heights were also investigated. Six distinct categories of aggregates were characterized in the 1 to 2-mm size fraction. The two most predominant categories were aggregates cemented by only Fe oxides and aggregates cemented by a mixture of Fe and Mn oxides. Iron-depleted aggregates, Fe and Mn-cemented sand aggregates, and root channel linings were also identified. The highest Fe content was in the root channel linings, and the highest Mn content was in the Fe/Mn cemented particles. Iron cemented aggregates were most common in surface horizons at all sites. Contaminant distribution varied between the Fe and Mn aggregates: As and Zn were positively correlated with aggregates with high concentrations of Fe, and Pb and Cd were positively correlated with aggregates with high concentrations of Mn.